I don’t see why it wouldn’t be legal. It doesn’t appear to be discrimination on the basis of any attribute that is restricted by law (e.g. sex, race, age, religion). You can’t legally enforce payment, but they’re not attempting to do that. It doesn’t appear to be a provider that may have a social or legislated requirement to provide service - such as an electricity provider.
This sounds personal, and borne out of being stung for $25,000. That apparently either hurt them significantly economically, emotionally, or both. I think I’d be pretty upset in their place - I know losing $25,000 would severely affect my business finances and my personal ones.
Let me share something personal to maybe help explain the mindset. A few years back one of my businesses was partnered with a builder to develop some adjoining house blocks and sell them. We’d done a couple, turned that over into a couple more, and so on. We held the title, luckily. Then, out of the blue, the builder goes insolvent and he declares bankruptcy personally. No notice or inkling given. It wasn’t our project that did it, but another part of his business. We were left with two unfinished houses. He’d received progress draws under finance - gone. Materials - gone. Subcontractors - gone.
I never heard from the builder, then or after. He apparently spoke to my brother at some point and said he felt so much better, and that going bankrupt was the best thing he ever did. He got growled at that that might be the case, but we were left holding his stinking mess. He slunk away with his tail between his legs.
It took us about 18 months to get through the insurance claim. It didn’t cover us for everything. We had to scramble to get things done. 18 months where we couldn’t work on the site led to degradation. Finishings had to be downgraded (the houses were in an upmarket area, and planned to be premium). Then there were the things the insurance didn’t cover, like landscaping and driveway (I think, from memory). Plus, the tradies we knew - from connection with the builder - lumped us in with him, and refused to work on the site. They wanted to be paid what they were owed too. Some we managed to convince, others we couldn’t.
We eventually managed to finish and sell the houses. All up we broke even - except for the extra 18 months of bank interest we had to wear. It took an insane amount of work, pleading, cajoling, and financial input from other business areas. Without all of that, we might have gone under too.
The point of all this is: If that builder came back to me today and said he’d pay cash, he wouldn’t even get to finish his sentence before he’d be out the door. If he compensated for the losses incurred, he might get to come back and pay cash but he wouldn’t be dealing with me.